When employed in a front wheel drive for a motor vehicle, the axis of the respective inner and outer rotatable members of the universal joint are oriented in inclined relationship relative to each other, both in dependence on the position and vertical movement of the vehicle wheels relative to the vehicle body and in dependence on the steering movement of the vehicle wheels relative to the longitudinal axis of the vehicle body. Conventionally, the outer rotatable member of the universal joint is affixed to the wheel hub with its axis of rotation lying in a substantially horizontal plane, and the axis of the inner rotatable member is inclined relative to that plane.
Due to the inclination of the axis of the inner rotable member relative to the axis of the outer rotatable member, the rollers carried by the trunnions of the inner rotatable member are caused to move in an orbital path upon rotation of the respective members, this requiring that the respective rollers move axially of the longitudinal grooves in the outer rotatable member to opposite sides of a median plane perpendicular to the axis of the outer rotatable member. Additionally, upon such movement of the rollers in one axial direction longitudinally of the grooves, the rollers must progressively slide axially of the trunnions in one direction, and, upon movement of the rollers axially of the grooves in the opposite direction, the rollers must progressively slide axially of the trunnions in a direction opposite to the first direction, the axial sliding movement of the rollers relative to the trunnion occuring in addition to pivotal movement of the rollers relative to the axis of the respective trunnions, such as occurs as a result of the rollers moving along linear paths which are inclined relative to the plane of movement of the axis of the respective trunnions.
At the time the rollers are moving axially outwardly along the trunnions, the frictional restraint on such movement results in a force being exerted on the rollers in a direction radially inwardly of the axis of the outer rotatable member, and conversely, upon movement of the rollers axially inwardly along the trunnion, the frictional restraint imposed on such movement results in a force being exerted on the rollers in a direction radially outwardly of the axis of the outer rotatable member.
Of necessity, and in order to eliminate simultaneous contact of the rollers with both of the opposed axial side walls of the longitudinal grooves in the outer rotatable member, the rollers intentionally are slightly undersized relative to the width of the longitudinal grooves, such that, under normal operating conditions, simultaneous contact of the roller with both side walls of the grooves cannot occur.
Such simultaneous contact must be avoided, in that axial movement of the respective rollers in one direction of rotation of the universal joint results in a rolling movement of the roller relative to one side wall of the groove, and a rotary movement of the roller relative to the opposite side wall of the groove in a direction which is opposite to that required for rolling motion of the roller relative to said opposite side wall.
For practical reasons, the opposite side walls of the longitudinal grooves are oppositely arcuately concave and, the outer periphery of the rollers are correspondingly convex, such that the rollers engage the associated side wall substantially in line engagement therewith.
While such an orientation of structure operates entirely successfully in the absence of forces exerted on the rollers in a direction radially inwardly or radially outwardly of the axis of the outer rotatable member, such as occurs only when the axes of the inner and outer rotatable members are aligned, in the presence of such radially inward or radially outward forces, there is a tendency for the rollers to climb up the associated side wall with a consequence that the diametrically opposite side of the roller will come into engagement with the opposite side wall.
The ability of the rollers to climb the associated side wall of the groove arises because the rollers are of a diameter slightly less than the width of the associated longitudinal groove and because there is a lack of restraint of movement of the rollers radially of the axis of the outer rotatable member.
Such a condition is entirely disadvantageous, in that simultaneous contact of the rollers with both of the groove side walls results in the roller being restrained against free rotation, accompanied by a consequential increase in the internal friction within the universal joint, the production of heat and noise within the universal joint, and abrasion or scuffing of the groove side walls and of the periphery of the rollers.